feat: add settings to adjust bitrate/quality

BetterCapture/Model/SettingsStore.swift

@@ -130,6 +130,46 @@ enum FrameRate: Int, CaseIterable, Identifiable {
     }
 }
 
+/// Video quality presets controlling compression bitrate for H.264 and HEVC.
+///
+/// Each preset defines a bits-per-pixel multiplier used to calculate the
+/// target average bitrate: `width * height * bpp * frameRate`.
+/// ProRes codecs ignore this setting since they use fixed-quality encoding.
+enum VideoQuality: String, CaseIterable, Identifiable {
+    case low = "Low"
+    case medium = "Medium"
+    case high = "High"
+
+    var id: String { rawValue }
+
+    /// Bits-per-pixel multiplier for H.264
+    var h264BitsPerPixel: Double {
+        switch self {
+        case .low:    0.05
+        case .medium: 0.1
+        case .high:   0.2
+        }
+    }
+
+    /// Bits-per-pixel multiplier for HEVC (more efficient codec)
+    var hevcBitsPerPixel: Double {
+        switch self {
+        case .low:    0.03
+        case .medium: 0.06
+        case .high:   0.1
+        }
+    }
+
+    /// Returns the bits-per-pixel multiplier for the given codec
+    func bitsPerPixel(for codec: VideoCodec) -> Double? {
+        switch codec {
+        case .h264: h264BitsPerPixel
+        case .hevc: hevcBitsPerPixel
+        case .proRes422, .proRes4444: nil
+        }
+    }
+}
+
 /// Persists user preferences using AppStorage
 @MainActor
 @Observable
@@ -146,6 +186,15 @@ final class SettingsStore {
         }
     }
 
+    var videoQuality: VideoQuality {
+        get {
+            VideoQuality(rawValue: videoQualityRaw) ?? .high
+        }
+        set {
+            videoQualityRaw = newValue.rawValue
+        }
+    }
+
     var videoCodec: VideoCodec {
         get {
             VideoCodec(rawValue: videoCodecRaw) ?? .hevc
@@ -516,6 +565,18 @@ final class SettingsStore {
         }
     }
 
+    private var videoQualityRaw: String {
+        get {
+            access(keyPath: \.videoQualityRaw)
+            return UserDefaults.standard.string(forKey: "videoQuality") ?? VideoQuality.high.rawValue
+        }
+        set {
+            withMutation(keyPath: \.videoQualityRaw) {
+                UserDefaults.standard.set(newValue, forKey: "videoQuality")
+            }
+        }
+    }
+
     private var videoCodecRaw: String {
         get {
             access(keyPath: \.videoCodecRaw)

BetterCapture/Service/AssetWriter.swift

@@ -368,6 +368,21 @@ final class AssetWriter: CaptureEngineSampleBufferDelegate, @unchecked Sendable
             videoSettings[AVVideoCodecKey] = AVVideoCodecType.proRes4444
         }
 
+        // Add compression properties for H.264 and HEVC to control bitrate.
+        // ProRes codecs use fixed-quality encoding and don't need these.
+        if let bpp = settings.videoQuality.bitsPerPixel(for: settings.videoCodec) {
+            let frameRate = settings.frameRate == .native ? 60.0 : Double(settings.frameRate.rawValue)
+            let bitrate = Int(size.width * size.height * bpp * frameRate)
+
+            videoSettings[AVVideoCompressionPropertiesKey] = [
+                AVVideoAverageBitRateKey: bitrate,
+                AVVideoExpectedSourceFrameRateKey: frameRate,
+                AVVideoMaxKeyFrameIntervalKey: Int(frameRate * 2)
+            ]
+
+            logger.info("Video compression: \(bitrate / 1_000_000) Mbps at \(Int(frameRate)) fps (\(settings.videoQuality.rawValue) quality)")
+        }
+
         // Add HDR color space settings for ProRes codecs with HDR enabled
         if settings.captureHDR && settings.videoCodec.supportsHDR {
             videoSettings[AVVideoColorPropertiesKey] = [

BetterCapture/View/SettingsView.swift

@@ -55,6 +55,14 @@ struct VideoSettingsView: View {
         }
     }
 
+    private var qualityHelpText: String {
+        if settings.videoQuality.bitsPerPixel(for: settings.videoCodec) != nil {
+            return "Controls the video bitrate. Higher quality produces sharper output with larger files"
+        } else {
+            return "ProRes codecs use fixed-quality encoding"
+        }
+    }
+
     var body: some View {
         Form {
             Section("Recording") {
@@ -82,6 +90,14 @@ struct VideoSettingsView: View {
                         Text(".\(format.rawValue)").tag(format)
                     }
                 }
+
+                Picker("Quality", selection: $settings.videoQuality) {
+                    ForEach(VideoQuality.allCases) { quality in
+                        Text(quality.rawValue).tag(quality)
+                    }
+                }
+                .disabled(settings.videoQuality.bitsPerPixel(for: settings.videoCodec) == nil)
+                .help(qualityHelpText)
             }
 
             Section("Advanced") {